1. Field of the Invention
The present invention is related to a door opener. More particularly, it relates to a door opener which can be used for closed-circuit current operation as well as for working current operation.
2. Discussion of the Background Art
A door opener of this kind is known, for example, from the U.S. patent application No. 08/808,161. This door opener can be used for closed-circuit operation as well as working circuit operation. In closed-circuit operation, the door latch is locked when a current flows through the electromagnet, and released when the current is switched off. In working current operation, the door latch is released when the current flows, while the door latch is locked when the current is switched off. The armature is movable between three consecutive positions placed in an order that corresponds to the series of conditions locked-released-locked or released-locked-released. However, the displacement path of the armature is delimited and selectively either the first or third stop position is blocked.
When there is a current flow through the electromagnet, the armature is either attracted toward the electromagnet or moves away from it. By selecting if the door latch is to be locked or released when the armature is attracted or moves away, the operation by means of a closed-circuit current or working current can be selected easily by displacing the stop element.
The electromagnet must be designed in such a way that the armature can move into all three positions, since otherwise a change from closed-circuit current operation to working current operation or vice versa would otherwise not be possible. This requires electromagnets with correspondingly large dimensions and capability. Such electromagnets are expensive and require door openers with sufficient space for installing the magnet.